Boy, I'm totally confused... My book is at work, but the way I read it was once you can do four sets of 15 second holds (here's the 60 second mark) then you move to the next progression. I also thought that Coach was recommending a total of 60 seconds of holds per workout.

For example if I can only hold a certain technique for five seconds with good form, then I need to do 12 rounds of it to get 60 seconds. The workouts go much faster as you get better because the holds are longer and the set count goes down really quickly.